Quantum Key Distribution at Terahertz Frequencies

The possibility of developing quantum computing machines that can break the widely used public-key cryptosystems has required us to look for new solutions to scenarios where long-term data security is needed. Quantum key distribution (QKD) is among the enabling techniques for providing such a level of data security and is being pursued by academic and commercial sectors alike to accelerate its ubiquitous use. Being reliant on few-photon communications, it has generally been perceived that implementing QKD in the optical domain is the most straightforward solution. However restricting this technology to the optical domain could make it more difficult to realise QKD when mobility and wireless access are required. This motivates us to consider using carrier signals at lower frequencies to enable wireless implementations of QKD. Being a few-photon communications system, there is, however, a fundamental barrier to using microwave frequencies for QKD, imposed by the requirement that the carrier photons must have higher, or similar energies, to the thermal background noise. This means that microwave and mm-wave frequencies would require prohibitively low temperature backgrounds. The terahertz regime, on the other hand, offers a regime of operation, where QKD can, in principle, be implemented. This interdisciplinary project has the goal of demonstrating a THz QKD system for the first time. This will be enabled by collaboration between our two well-established theory and experimental groups in quantum communications and THz technologies.